Physical activity researchers working with preschool-age children have identified a need for a three-axis activity monitor (actigraph) to quantitatively measure these children's activity. Present day activity monitors are either uni-direction or too bulky to be worn by this age group. Development of a miniature triaxial activity monitor is proposed to meet the needs of these researchers. Preliminary work with IC-sized accelerometers demonstrated the concept of a miniature (5.1 X 3.8 X 1.5cm, 43 grams) three-axis activity monitor was feasible. We propose to develop a prototype three-axis device and determine its reliability and validity for this application through laboratory and field-testing on preschool children. The improvements to present day devices will include implementing all signal processing with digital filters within the software, The new device will use a microcontroller having FLASH memory and employ a solid-state accelerometer with a DC response so that simple procedures using only gravity can be used to calibrate the device. The new device resulting from this effort will be adaptable to many applications in the physical activity monitoring and physical rehabilitation healthcare community. PROPOSED COMMERCIAL APPLICATION: The tri-axial activity monitor will have many applications in the healthcare field. Some of these include: monitoring patterns of physical activity to assess healthful lifestyles, monitoring adherence to physical rehabilitation regimens, and assessing the effectiveness of treatment methods for diseases such as patidnsons, chronic fatigue, depression, and sleep disorders.